The present invention relates to a marine fish farm for cultivating fish in an intensive system to obtain an optimum productivity and a maximum simplification in cleaning of the netting, derived from the possibility of locating the fish farm at the depth and marine area.
The methods in the field of aquaculture which are commonly called "marine farms" have, to date, been employing three systems, namely, extensive, semi-intensive and intensive.
The extensive system consists in enclosing the fish, crustaceans and mollusks in ponds, marshes, yards or large enclosures, where the fish, at a very low density, must obtain food on their own, i.e., from their environment and when they reach the commercial stage they are fished for their commercialization. Obviously, productivity in this system is low since cultivations must bear loads of approximately 100/200 kg. of fish per hectare per year.
The semi-extensive system is similar to the intensive system, with the sole difference that it provides more food for the fish, affording cultivation loads which increase to 2000/5000 kg. of fish per hectare per year.
Finally, the intensive system consists in enclosing a large group of fish in a small pond made of cement, plastic, or any other suitable material, where fish are submitted to large streams of water, which require feeding, etc., and where fish may be cultivated with high density. Such system have cultivation loads of approximately 300,000 kg of fish per hectare per year.
Thus, it is obvious that the intensive system prevails with respect to the two other systems described hereinabove.
In countries with a longer marine aquaculture tradition, such as Japan and Norway, small floating cages have been installed in more sheltered areas of bays, fiords, lagoons, etc. However, the deficiency of oxygen, high temperature fluctuations, concentration of residues, outcrop of seaweed, etc. have gradually caused more open and deeper areas to be sought. Furthermore, the cages have been designed to withstand the dynamic efforts of areas with scarce shelter to be used.
The trend observed in the countries, where aquaculture is more developed, consists in increasingly using large cages, placing them away from sheltered areas in the areas which are more exposed to the dynamic effects of the waves. This is obviously due to the fact that sheltered areas have smaller flows of water, are shallower, and the decay of fiords affects the cultivation system, depriving it of oxygen and poisoning it with the production of hydrogen suflide; temperature fluctuations are very high, with the consequent risk of diseases. In such countries it may be observed that year after year fish farms are moved to deeper areas, but due to the many fiords and internal seas, as well as to the slow development of aquaculture, such sheltered areas essentially meet the current needs.
Thus, the aforementioned problems, plus the fact that fish live in the sea and must obviously be reared in the sea, show that this is the most ideal location for fish farms, and the deeper locations are the better ones.
Fish farms are known, which includes large floating platforms from which hang and are submerged in water one or many cages which contain the fish being cultivated. The cages are made from netting. However, this method, albeit solving the aforementioned problems and relating to installations in sheltered areas, gives rise to new and by no means insignificant problems.
Specifically the waves to which the fish farm will be permanently submitted, require that the fish farm same to be substantially oversized. Attention is to be called in this sense to the fact that, in deep water, waves can reach heights of 22 m. and periods of 16 seconds whereby the fish farms must have the structural strength but they also have the limitation as regards their dimensions.
On the other hand, these floating installations imply that fish grow in a surface area where there are very considerable temperature fluctuations, both as regards time and as regards the sea area in which requires that the fish farm be located in a specific place, which is most suitable for the optimum range of temperatures of a specific species of fish. And furthermore, an effect called thermocline which consists in that the surface water layer is heated as a result of solar radiation, which gives rise to a strip of approximately 30 m. of warm water, essentially takes place in the summer, fish swim in the upper area of the thermocline. In the autumn, and due to the action of the waves, the water tends to be uniform, the temperature tending to decrease towards that at the sea floor. The water is consequently formed of different layers or strata down to 50/70 m., and from this depth the water temperature tends to be uniform. These changes in the water temperature are very harmful fish since it depletes their defenses vis-a-vis diseases.
Finally, the surface layer of the water, particularly due to solar heating, affords the most suitable conditions for the growth of seaweed, which tend to block the netting which surrounding the fish, wherefore the frequency and intensity of cleaning operations is very important, for, because in an intensive cultivation, it is necessary that the netting be kept perfectly clean in order that the water inside the fish farm be constantly renewed, to ensure a constant suitable level of oxygenation.